1. Field of the Invention
The present invention relates to a particle monitor system and a substrate processing apparatus, and more particularly, to a particle monitor system for detecting the number of particles flowing through an exhaust pipe of a substrate processing apparatus, and a substrate processing apparatus including the same.
2. Description of the Related Art
A substrate processing apparatus is known that includes a chamber for housing a wafer as substrate and an exhaust pipe for discharging particles and gases from the chamber. In this apparatus, a plasma is generated in the chamber and used to perform desired plasma processing on a wafer. While the plasma processing is repeatedly performed, particles resulting from reaction products and/or deposits are generated in the chamber. With the increasing number of particles in the chamber, particles adhered to wafers increases, resulting in a low yield of semiconductor devices from wafers. It is therefore necessary to regularly detect the number of particles in the chamber and clean the interior of the chamber when the number of particles exceeds a predetermined threshold value.
As a method for detecting the number of particles in the chamber, it is known to detect the number of particles in a sub-chamber, which is provided adjacent to the chamber (see Japanese Laid-open Patent Publication No. 9-203704), or detect the number of particles flowing through an exhaust pipe, and estimate the number of particles in the chamber based on a result of the detection.
An ISPM (In Situ Particle Monitor) is usually used for the detection of the number of particles in the sub-chamber or the exhaust pipe. For example, the ISPM includes a laser oscillator for irradiating laser light toward inside the exhaust pipe, a photo multiplier tube (PMT) for observing light scattered by particles passing through the laser light, and a PC for detecting the number of particles in the chamber based on the intensity of observed scattered light and so on.
In the ISPM, since the laser light irradiated to the inside of the exhaust pipe is narrow in width, particles passing through the laser light are only part of the particles flowing inside the exhaust pipe, thus making it impossible to accurately detect the number of particles flowing through the exhaust pipe. To obviate this, methods have been developed, in which laser light is broadened into a belt shape to irradiate the entire section of the exhaust pipe or the inside of the exhaust pipe is scanned by laser light, so that most of particles flowing through the exhaust pipe are made to pass through the laser light.
In the method of broadening laser light into a belt shape, however, scattered light is low in intensity, which makes it difficult to detect minute particles. On the other hand, in the method of scanning the inside of the exhaust pipe with laser light, particles flowing at high speeds can sometimes pass through that region of the exhaust pipe which is scanned with the laser light, without crossing the laser light. Thus, some of the particles flowing at high speeds cannot be detected. In addition, since there are produced stray light and noise at the time of scanning, it is sometimes determined that particles had passed through the laser light even though particles do not actually pass therethrough. In other words, it is still difficult to accurately detect the number or size of particles flowing through the exhaust pipe.